The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred to as user equipments (UEs). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. With the optimization of the network design, many improvements have developed over the evolution of various standards.
When UE needs to establish a connection for service, UE sends a SERVICE REQUEST message to a mobility management entity (MME) via its serving eNB. UE also establish user plane radio bearers for data communication. The service request procedure is considered completed when 1) UE receives a security-protected non-access stratum (NAS) message, e.g. a SECURITY MODE COMMAND message or a SERVICE ACCEPT message, or 2) UE receives an indication from lower layers that the user plane radio bearers are setup. If the service request procedure is considered completed in the UE and the UE receives a SERVICE ACCEPT message afterwards, different methods have been provided.
In Rel-13, the UE considers the SERVICE ACCEPT message is received in wrong protocol state. The network cannot always successfully send SERVICE ACCEPT message to the UE with evolved packet system (EPS) bearer context status information element and the bearer context status information is not synchronized in the UE. In Rel-14, the UE is able to receive and treat a SERVICE ACCEPT message after the service request procedure is determined successfully completed, i.e., after the UE has already received SECURITY MODE COMMAND message or been indicated that the user plane radio bearers are set up. In this special case, the UE shall treat the SERVICE ACCEPT message as it would have been received during the service request procedure, but in all other cases the UE shall still consider the SERVICE ACCEPT message is received in wrong protocol state.
It is not defined of how long after the service request procedure is completed the UE shall accept the SERVICE ACCEPT message, i.e., what is the time window to allow the SERVICE ACCEPT message been successfully received after the service request procedure is completed. A solution is sought.